Wet-chemical synthesis of AgCo@CQAS nanozyme: a novel high-activity copper-free laccase mimic for sensitive hydrogel-based pesticide detection.

Beyond peroxidase- and oxidase-like activities, the laccase-like activity of nanozymes has gradually gained significant attention. However, the catalytic performance of current copper-containing or non-copper laccase mimics remains relatively low, limiting their broader application. Inspired by the structure and properties of natural laccase, this study employed silver (Ag) and cobalt (Co) as catalytic active center, Prussian blue analog K3Co(CN)6 as ligand, and chitosan quaternary ammonium salt (CQAS) as electron transmitter, developed a novel copper-free laccase mimic, AgCo@CQAS, via a wet-chemical method. The features Ag0, Co2+, and Co3+ coordinated with nitrogen atoms, structurally mimicking the catalytic active center of laccase. Combined with the charge characteristics, hydrophilicity, and electron transfer capability of CQAS, these components exhibit a remarkably similar function to the T1 copper, T2 copper, and T3 copper sites in laccase. Like the natural laccase, the AgCo@CQAS catalytic process consumes O2 without producing H2O2, while generating semiquinone radicals and superoxide anion. Notably, AgCo@CQAS demonstrates superior stability and kinetic parameters compared to laccase. When applied to develop a hydrogel sensor for Lambda-cyhalothrin detection, a significantly lower limit of detection (0.11 μg L-1) was achieved. This sensor also exhibited excellent sensitivity, anti-interference capability, stability, and low variability. Crucially, the hydrogel sensor demonstrated detection performance comparable to the national standard method.